WASHINGTON – The Joint Plan of Action allows Iran to continue research and development on nuclear centrifuge technology, senior US administration officials said on Sunday, announcing the conclusion of technical talks on the implementation of an interim deal pausing Iran’s nuclear program.

The deal, brokered by world powers in Geneva in November, is to go into effect on January 20 and to last for six months while Iran and the P5+1 – the United States, United Kingdom, France, Russia, China and Germany – attempt to negotiate a comprehensive agreement to end the long-standing crisis.

“[Iran’s] commitment is to continue their current enrichment R&D practices,” a senior official told journalists in a phone conference on Sunday, detailing the agreement. “That’s been documented. That’s what they’ll continue to do.”

The Prime Minister’s Office had no response to the announcement that the deal will come into effect next week, even though Jerusalem was harshly critical of the agreement when it was first signed in November.

Before the deal was reached in the fall, Iran had begun installing new IR2M centrifuges that experts believe are five times more efficient at enriching uranium. Iranian officials have publicly asserted they wish to advance their efficacy.

Research into advanced centrifuge technology caused the implementation talks to run longer than expected.

But Iran cited a provision in the Joint Plan of Action that explicitly allows Iran to continue existing research – “what you would do with a piece of paper,” versus what one can implement and produce, the senior official said.

“One can always imagine other things, but that was the arrangement that was made,” he added, when asked if the administration had hoped for a pause to the research into new centrifuge technology.

“This will be a subject for the comprehensive resolution.”

But the administration believes the chances of reaching such a comprehensive agreement stands at “50-50,” the official said, echoing tepid optimism voiced by US President Barack Obama last month.

Details of the technical agreement have been submitted to the United Nations International Atomic Energy Agency in Vienna.

Obama said on Sunday that Iran would “limit its enrichment capability by not installing or starting up additional centrifuges or using next-generation centrifuges,” and would “start eliminating its stockpile of higher levels of enriched uranium and dismantling some of the infrastructure that makes such enrichment possible.”

Iran cannot install or fuel new centrifuges, and will unhinge centrifuge lines working in sync to enrich uranium – previously to 20 percent, a key step in the enrichment process toward weaponizing fissile material.

“With today’s agreement, we have made concrete progress,” Obama said. “I have no illusions about how hard it will be to achieve this objective, but for the sake of our national security and the peace and security of the world, now is the time to give diplomacy a chance to succeed.”

US Secretary of State John Kerry said that comprehensive nuclear talks would be a “far greater challenge.”

“The $4.2 billion in restricted Iranian assets that Iran will gain access to as part of the agreement will be released in regular installments throughout the six months,” Kerry said on Sunday. “The final installment will not be available to Iran until the very last day.”

Officials did not say that Congress was a topic of conversation among the P5+1 and Iran during the technical talks. But US intelligence estimates that Iran’s leaders mean what they say in warning the Senate against passing a sanctions bill, introduced just before Christmas last month.

The bill, with 60 cosponsors, would prepare sanctions on Iran should international powers fail to reach a comprehensive deal, or should Iran disobey tenets of the interim agreement.

Obama has threatened to veto the bill.

“Our intelligence community has assessed that new sanctions enacted during negotiations are likely to derail the negotiations,” a second senior official said. “The stakes are very high here.”